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</a></div> <!----></nav>  <ul class="sidebar-links"><li><a href="/fe/" aria-current="page" class="sidebar-link">大前端学习路径 + B站资源整合</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>CSS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>JavaScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ES6</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Vue3</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/fe/vue3/" aria-current="page" class="sidebar-link">面试官：Vue3.0的设计目标是什么？做了哪些优化</a></li><li><a href="/fe/vue3/vue3_vue2.html" class="sidebar-link">面试官：vue3有了解过吗？能说说跟vue2的区别吗？</a></li><li><a href="/fe/vue3/performance.html" aria-current="page" class="active sidebar-link">面试官：Vue3.0性能提升主要是通过哪几方面体现的？</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/fe/vue3/performance.html#一、编译阶段" class="sidebar-link">一、编译阶段</a></li><li class="sidebar-sub-header"><a href="/fe/vue3/performance.html#二、源码体积" class="sidebar-link">二、源码体积</a></li><li class="sidebar-sub-header"><a href="/fe/vue3/performance.html#三、响应式系统" class="sidebar-link">三、响应式系统</a></li><li class="sidebar-sub-header"><a href="/fe/vue3/performance.html#参考文献" class="sidebar-link">参考文献</a></li></ul></li><li><a href="/fe/vue3/proxy.html" class="sidebar-link">面试官：Vue3.0里为什么要用 Proxy API 替代 defineProperty API ？</a></li><li><a href="/fe/vue3/composition.html" class="sidebar-link">面试官：Vue3.0 所采用的 Composition Api 与 Vue2.x 使用的 Options Api 有什么不同？</a></li><li><a href="/fe/vue3/treeshaking.html" class="sidebar-link">面试官：说说Vue 3.0中Treeshaking特性？举例说明一下？</a></li><li><a href="/fe/vue3/modal_component.html" class="sidebar-link">面试官：用Vue3.0 写过组件吗？如果想实现一个 Modal你会怎么设计？</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="面试官-vue3-0性能提升主要是通过哪几方面体现的"><a href="#面试官-vue3-0性能提升主要是通过哪几方面体现的" class="header-anchor">#</a> 面试官：Vue3.0性能提升主要是通过哪几方面体现的？</h1> <p><img src="https://static.vue-js.com/2aac1020-5ed0-11eb-ab90-d9ae814b240d.png" alt=""></p> <h2 id="一、编译阶段"><a href="#一、编译阶段" class="header-anchor">#</a> 一、编译阶段</h2> <p>回顾<code>Vue2</code>，我们知道每个组件实例都对应一个 <code>watcher</code> 实例，它会在组件渲染的过程中把用到的数据<code>property</code>记录为依赖，当依赖发生改变，触发<code>setter</code>，则会通知<code>watcher</code>，从而使关联的组件重新渲染</p> <p><img src="https://static.vue-js.com/39066120-5ed0-11eb-85f6-6fac77c0c9b3.png" alt=""></p> <p>试想一下，一个组件结构如下图</p> <div class="language-html extra-class"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>template</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>content<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>静态文本<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>静态文本<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>{{ message }}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>静态文本<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
        ...
        <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>text<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>静态文本<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>template</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><p>可以看到，组件内部只有一个动态节点，剩余一堆都是静态节点，所以这里很多 <code>diff</code> 和遍历其实都是不需要的，造成性能浪费</p> <p>因此，<code>Vue3</code>在编译阶段，做了进一步优化。主要有如下：</p> <ul><li>diff算法优化</li> <li>静态提升</li> <li>事件监听缓存</li> <li>SSR优化</li></ul> <h4 id="diff算法优化"><a href="#diff算法优化" class="header-anchor">#</a> diff算法优化</h4> <p><code>vue3</code>在<code>diff</code>算法中相比<code>vue2</code>增加了静态标记</p> <p>关于这个静态标记，其作用是为了会发生变化的地方添加一个<code>flag</code>标记，下次发生变化的时候直接找该地方进行比较</p> <p>下图这里，已经标记静态节点的<code>p</code>标签在<code>diff</code>过程中则不会比较，把性能进一步提高</p> <p><img src="https://static.vue-js.com/c732e150-5c58-11eb-ab90-d9ae814b240d.png" alt=""></p> <p>关于静态类型枚举如下</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">const</span> <span class="token keyword">enum</span> PatchFlags <span class="token punctuation">{</span>
  <span class="token constant">TEXT</span> <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">,</span><span class="token comment">// 动态的文本节点</span>
  <span class="token constant">CLASS</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">1</span><span class="token punctuation">,</span>  <span class="token comment">// 2 动态的 class</span>
  <span class="token constant">STYLE</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">2</span><span class="token punctuation">,</span>  <span class="token comment">// 4 动态的 style</span>
  <span class="token constant">PROPS</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">3</span><span class="token punctuation">,</span>  <span class="token comment">// 8 动态属性，不包括类名和样式</span>
  <span class="token constant">FULL_PROPS</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">4</span><span class="token punctuation">,</span>  <span class="token comment">// 16 动态 key，当 key 变化时需要完整的 diff 算法做比较</span>
  <span class="token constant">HYDRATE_EVENTS</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">5</span><span class="token punctuation">,</span>  <span class="token comment">// 32 表示带有事件监听器的节点</span>
  <span class="token constant">STABLE_FRAGMENT</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">6</span><span class="token punctuation">,</span>   <span class="token comment">// 64 一个不会改变子节点顺序的 Fragment</span>
  <span class="token constant">KEYED_FRAGMENT</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token comment">// 128 带有 key 属性的 Fragment</span>
  <span class="token constant">UNKEYED_FRAGMENT</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">8</span><span class="token punctuation">,</span> <span class="token comment">// 256 子节点没有 key 的 Fragment</span>
  <span class="token constant">NEED_PATCH</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">9</span><span class="token punctuation">,</span>   <span class="token comment">// 512</span>
  <span class="token constant">DYNAMIC_SLOTS</span> <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">&lt;&lt;</span> <span class="token number">10</span><span class="token punctuation">,</span>  <span class="token comment">// 动态 solt</span>
  <span class="token constant">HOISTED</span> <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">,</span>  <span class="token comment">// 特殊标志是负整数表示永远不会用作 diff</span>
  <span class="token constant">BAIL</span> <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">2</span> <span class="token comment">// 一个特殊的标志，指代差异算法</span>
<span class="token punctuation">}</span>
</code></pre></div><h4 id="静态提升"><a href="#静态提升" class="header-anchor">#</a> 静态提升</h4> <p><code>Vue3</code>中对不参与更新的元素，会做静态提升，只会被创建一次，在渲染时直接复用</p> <p>这样就免去了重复的创建节点，大型应用会受益于这个改动，免去了重复的创建操作，优化了运行时候的内存占用</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token operator">&lt;</span>span<span class="token operator">&gt;</span>你好<span class="token operator">&lt;</span><span class="token operator">/</span>span<span class="token operator">&gt;</span>

<span class="token operator">&lt;</span>div<span class="token operator">&gt;</span><span class="token punctuation">{</span><span class="token punctuation">{</span> message <span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token operator">&lt;</span><span class="token operator">/</span>div<span class="token operator">&gt;</span>
</code></pre></div><p>没有做静态提升之前</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token parameter">_ctx<span class="token punctuation">,</span> _cache<span class="token punctuation">,</span> $props<span class="token punctuation">,</span> $setup<span class="token punctuation">,</span> $data<span class="token punctuation">,</span> $options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token function">_openBlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">_createBlock</span><span class="token punctuation">(</span>_Fragment<span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">[</span>
    <span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;span&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token string">&quot;你好&quot;</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
    <span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;div&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token function">_toDisplayString</span><span class="token punctuation">(</span>_ctx<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token comment">/* TEXT */</span><span class="token punctuation">)</span>
  <span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token number">64</span> <span class="token comment">/* STABLE_FRAGMENT */</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>做了静态提升之后</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> _hoisted_1 <span class="token operator">=</span> <span class="token comment">/*#__PURE__*/</span><span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;span&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token string">&quot;你好&quot;</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">1</span> <span class="token comment">/* HOISTED */</span><span class="token punctuation">)</span>

<span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token parameter">_ctx<span class="token punctuation">,</span> _cache<span class="token punctuation">,</span> $props<span class="token punctuation">,</span> $setup<span class="token punctuation">,</span> $data<span class="token punctuation">,</span> $options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token function">_openBlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">_createBlock</span><span class="token punctuation">(</span>_Fragment<span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">[</span>
    _hoisted_1<span class="token punctuation">,</span>
    <span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;div&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token function">_toDisplayString</span><span class="token punctuation">(</span>_ctx<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token comment">/* TEXT */</span><span class="token punctuation">)</span>
  <span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token number">64</span> <span class="token comment">/* STABLE_FRAGMENT */</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>

<span class="token comment">// Check the console for the AST</span>
</code></pre></div><p>静态内容<code>_hoisted_1</code>被放置在<code>render</code> 函数外，每次渲染的时候只要取 <code>_hoisted_1</code> 即可</p> <p>同时 <code>_hoisted_1</code> 被打上了 <code>PatchFlag</code> ，静态标记值为 -1 ，特殊标志是负整数表示永远不会用于 Diff</p> <h4 id="事件监听缓存"><a href="#事件监听缓存" class="header-anchor">#</a> 事件监听缓存</h4> <p>默认情况下绑定事件行为会被视为动态绑定，所以每次都会去追踪它的变化</p> <div class="language-text extra-class"><pre class="language-text"><code>&amp;lt;div&gt;
  &amp;lt;button @click = 'onClick'&gt;点我&amp;lt;/button&gt;
&amp;lt;/div&gt;
</code></pre></div><p>没开启事件监听器缓存</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">const</span> render <span class="token operator">=</span> <span class="token comment">/*#__PURE__*/</span><span class="token function">_withId</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token parameter">_ctx<span class="token punctuation">,</span> _cache<span class="token punctuation">,</span> $props<span class="token punctuation">,</span> $setup<span class="token punctuation">,</span> $data<span class="token punctuation">,</span> $options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token function">_openBlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">_createBlock</span><span class="token punctuation">(</span><span class="token string">&quot;div&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">[</span>
    <span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;button&quot;</span><span class="token punctuation">,</span> <span class="token punctuation">{</span> onClick<span class="token operator">:</span> _ctx<span class="token punctuation">.</span>onClick <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token string">&quot;点我&quot;</span><span class="token punctuation">,</span> <span class="token number">8</span> <span class="token comment">/* PROPS */</span><span class="token punctuation">,</span> <span class="token punctuation">[</span><span class="token string">&quot;onClick&quot;</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
                                             <span class="token comment">// PROPS=1&lt;&lt;3,// 8 //动态属性，但不包含类名和样式</span>
  <span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre></div><p>开启事件侦听器缓存后</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token parameter">_ctx<span class="token punctuation">,</span> _cache<span class="token punctuation">,</span> $props<span class="token punctuation">,</span> $setup<span class="token punctuation">,</span> $data<span class="token punctuation">,</span> $options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token function">_openBlock</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token function">_createBlock</span><span class="token punctuation">(</span><span class="token string">&quot;div&quot;</span><span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token punctuation">[</span>
    <span class="token function">_createVNode</span><span class="token punctuation">(</span><span class="token string">&quot;button&quot;</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
      onClick<span class="token operator">:</span> _cache<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">||</span> <span class="token punctuation">(</span>_cache<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>args</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">(</span>_ctx<span class="token punctuation">.</span><span class="token function">onClick</span><span class="token punctuation">(</span><span class="token operator">...</span>args<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token string">&quot;点我&quot;</span><span class="token punctuation">)</span>
  <span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p>上述发现开启了缓存后，没有了静态标记。也就是说下次<code>diff</code>算法的时候直接使用</p> <h4 id="ssr优化"><a href="#ssr优化" class="header-anchor">#</a> SSR优化</h4> <p>当静态内容大到一定量级时候，会用<code>createStaticVNode</code>方法在客户端去生成一个static node，这些静态<code>node</code>，会被直接<code>innerHtml</code>，就不需要创建对象，然后根据对象渲染</p> <div class="language-js extra-class"><pre class="language-js"><code>div<span class="token operator">&gt;</span>
	<span class="token operator">&lt;</span>div<span class="token operator">&gt;</span>
		<span class="token operator">&lt;</span>span<span class="token operator">&gt;</span>你好<span class="token operator">&lt;</span><span class="token operator">/</span>span<span class="token operator">&gt;</span>
	<span class="token operator">&lt;</span><span class="token operator">/</span>div<span class="token operator">&gt;</span>
	<span class="token operator">...</span>  <span class="token comment">// 很多个静态属性</span>
	<span class="token operator">&lt;</span>div<span class="token operator">&gt;</span>
		<span class="token operator">&lt;</span>span<span class="token operator">&gt;</span><span class="token punctuation">{</span><span class="token punctuation">{</span> message <span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token operator">&lt;</span><span class="token operator">/</span>span<span class="token operator">&gt;</span>
	<span class="token operator">&lt;</span><span class="token operator">/</span>div<span class="token operator">&gt;</span>
<span class="token operator">&lt;</span><span class="token operator">/</span>div<span class="token operator">&gt;</span>
</code></pre></div><p>编译后</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> mergeProps <span class="token keyword">as</span> _mergeProps <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">&quot;vue&quot;</span>
<span class="token keyword">import</span> <span class="token punctuation">{</span> ssrRenderAttrs <span class="token keyword">as</span> _ssrRenderAttrs<span class="token punctuation">,</span> ssrInterpolate <span class="token keyword">as</span> _ssrInterpolate <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">&quot;@vue/server-renderer&quot;</span>

<span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">ssrRender</span><span class="token punctuation">(</span><span class="token parameter">_ctx<span class="token punctuation">,</span> _push<span class="token punctuation">,</span> _parent<span class="token punctuation">,</span> _attrs<span class="token punctuation">,</span> $props<span class="token punctuation">,</span> $setup<span class="token punctuation">,</span> $data<span class="token punctuation">,</span> $options</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">const</span> _cssVars <span class="token operator">=</span> <span class="token punctuation">{</span> style<span class="token operator">:</span> <span class="token punctuation">{</span> color<span class="token operator">:</span> _ctx<span class="token punctuation">.</span>color <span class="token punctuation">}</span><span class="token punctuation">}</span>
  <span class="token function">_push</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">&lt;div</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>
    <span class="token function">_ssrRenderAttrs</span><span class="token punctuation">(</span><span class="token function">_mergeProps</span><span class="token punctuation">(</span>_attrs<span class="token punctuation">,</span> _cssVars<span class="token punctuation">)</span><span class="token punctuation">)</span>
  <span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">&gt;&lt;div&gt;&lt;span&gt;你好&lt;/span&gt;...&lt;div&gt;&lt;span&gt;你好&lt;/span&gt;&lt;div&gt;&lt;span&gt;</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>
    <span class="token function">_ssrInterpolate</span><span class="token punctuation">(</span>_ctx<span class="token punctuation">.</span>message<span class="token punctuation">)</span>
  <span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">&lt;/span&gt;&lt;/div&gt;&lt;/div&gt;</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><h2 id="二、源码体积"><a href="#二、源码体积" class="header-anchor">#</a> 二、源码体积</h2> <p>相比<code>Vue2</code>，<code>Vue3</code>整体体积变小了，除了移出一些不常用的API，再重要的是<code>Tree shanking</code></p> <p>任何一个函数，如<code>ref</code>、<code>reavtived</code>、<code>computed</code>等，仅仅在用到的时候才打包，没用到的模块都被摇掉，打包的整体体积变小</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> computed<span class="token punctuation">,</span> defineComponent<span class="token punctuation">,</span> ref <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'vue'</span><span class="token punctuation">;</span>
<span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token function">defineComponent</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    <span class="token function">setup</span><span class="token punctuation">(</span><span class="token parameter">props<span class="token punctuation">,</span> context</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">const</span> age <span class="token operator">=</span> <span class="token function">ref</span><span class="token punctuation">(</span><span class="token number">18</span><span class="token punctuation">)</span>

        <span class="token keyword">let</span> state <span class="token operator">=</span> <span class="token function">reactive</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
            name<span class="token operator">:</span> <span class="token string">'test'</span>
        <span class="token punctuation">}</span><span class="token punctuation">)</span>

        <span class="token keyword">const</span> readOnlyAge <span class="token operator">=</span> <span class="token function">computed</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> age<span class="token punctuation">.</span>value<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token comment">// 19</span>

        <span class="token keyword">return</span> <span class="token punctuation">{</span>
            age<span class="token punctuation">,</span>
            state<span class="token punctuation">,</span>
            readOnlyAge
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="三、响应式系统"><a href="#三、响应式系统" class="header-anchor">#</a> 三、响应式系统</h2> <p><code>vue2</code>中采用 <code>defineProperty</code>来劫持整个对象，然后进行深度遍历所有属性，给每个属性添加<code>getter</code>和<code>setter</code>，实现响应式</p> <p><code>vue3</code>采用<code>proxy</code>重写了响应式系统，因为<code>proxy</code>可以对整个对象进行监听，所以不需要深度遍历</p> <ul><li>可以监听动态属性的添加</li> <li>可以监听到数组的索引和数组<code>length</code>属性</li> <li>可以监听删除属性</li></ul> <p>关于这两个 API 具体的不同，我们下篇文章会进行一个更加详细的介绍</p> <h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>https://juejin.cn/post/6903171037211557895</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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